This introductory chapter sets the stage for the chapters to come in this book. It provides a definition of advertising and briefly sketches its history. In addition, in this chapter we discuss the key functions of advertising, ranging from societal functions such as facilitating competition among firms, funding mass media and serving as a key employer to thousands of professionals worldwide to individual functions, which are twofold: to inform and persuade consumers. We situate advertising amid other promotion mix elements and we discuss various approaches to conceptualizing advertising effects. There are two basic approaches to the conceptualization of the effects of advertising: the modelling approach and the behavioural approach. The modelling approach focuses on the aggregate level and relates advertising inputs (e.g. expenditures) to outputs (e.g. sales). The behavioural approach focuses on individual responses to specific advertising elements. We then further zoom in on the particular lens adopted in this book: the psychological approach to advertising’s impact, aiming to identify effects of specific advertising stimuli on particular individual responses and elucidating the processes responsible for any effects. We briefly discuss the different types of effects that advertising can have on consumer cognition, emotion and behaviour and we highlight how a major development in the behavioural sciences – the so called ‘replication crisis’ – has affected (the interpretation of) psychological research in general and the psychology of advertising in particular.